Re: [LAD] AoIP question

Winfried Ritsch:
> Am Sonntag, 5. Oktober 2014, 23:35:21 schrieb tom@trellis.ch:
> > On Sun, October 5, 2014 22:25, Fons Adriaensen wrote:
> > > On Sun, Oct 05, 2014 at 08:39:11PM +0200, tom@trellis.ch wrote:
> > >> As a scenario, at point a) an analog signal is injected that will be
> > >> played back (analog) at point b) with the lowest possible (and constant)
> > >>
> > >> latency. How do you intend to handle diverging clocks of the audio
> > >>
> > >> interfaces (ADC/DAC) at both (a/b) ends?
> > >
> > > Either
> > >
> > >
> > > 1. Sync the HW sample rates to an explicit or implicit reference
> > > provided by the network protocol. Requires special audio HW. A few normal
> > > audio interfaces (e.g. some RME cards) would allow to do this as well, but
> > > I know of no software that uses this
> > > capability.
> >
> > Sounds interesting. I asked myself if it would be possible to drive the
> > audio interface clock by the host (not by a wordclock coming from another
> > audio interface which makes the "network" case local again to some
> > degree), i.e. through ticks sent via FW/USB.
> >
> just to add another options and be a wiseacre :
>
> On a microchip dsPIC [1] you can adjust the internal oscillator (RC) (where
> also the sample clock for DA is derived) in a small range of 10%, so it is
> possible to use PTP for sample-exact synchronization (I did do a "soft PLL"
> for a low cost solution of a DA to avoid re-sampling and big buffers). I was
> told on ARMs Oscillator tuning is also possible, and if audiohardware derives
> clocks from it, it can also be tuned and used as soft PLL.

The arm's I used ([b]) have an PLL at the clock input and a few multiplier
and prescalers, so if you have a clock from a PTP tranceiver ([a] have
a clock output of 125MHz scaled down by 2..255). So sync. should be
possible.

According to {b] p.939, they (if they have ethernet) supports PTP directly.

> Anyway there are Chips [2] which can generate sample-clocks (Master-Clock)
> from a PTP signal, so if your audiohardware supports Master-Clock, you can add
> such a chip ;-).
...
> [1] http://ww1.microchip.com/downloads/en/DeviceDoc/39700c.pdf page 10
> [2] http://en.wikipedia.org/wiki/List_of_PTP_implementations#silicon

I only found [a], perhaps another distributer.

//// {another mail}

> http://www.rtnet.org/

Thanks for the link.

Regards,
/Karl Hammar

[a] http://se.farnell.com/texas-instruments/dp83640tvv-nopb/ic-ethernet-cont-ieee802-3-100mbps/dp/2308696
[b] http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/REFERENCE_MANUAL/CD00171190.pdf

-----------------------------------------------------------------------
Aspö Data
Lilla Aspö 148
S-742 94 Östhammar
Sweden
+46 173 140 57

_______________________________________________
Linux-audio-dev mailing list
Linux-audio-dev@lists.linuxaudio.org
http://lists.linuxaudio.org/listinfo/linux-audio-dev
Received on Sat Oct 11 04:15:03 2014